There is a cure for your daughters condition. Have a Doc prescribe her around 40 MG of Dexedrine a day, combined with a high dose of an SNRI (Wellbutrin or Effexor XR).
Considering you have ADD and the fact that it IS without a single doubt hereditary, there's a pretty strong chance that her "condition" has been diagnosed as a personality trait rather than what it really is (a neurological deficit).
ADD in girls is usually of the inattentive type and most therapists will overlook it and label her currently poor coping skills as a personality disorder.
I cannot stress you enough that therapy alone will only bring her more frustration and in return only exasperate her condition.
Therapy alone is worthless.
You will never ever "Cure" someone who suffers from ADD without treating the underlying neurological condition.
(That and might want to get your nephew off of the goddamn lithium, geodon or whatever ilk they're pushing him.)